Sewing machine for automatic backtacking

ABSTRACT

A sewing machine for automatically making a backtacking stitch against unstitching at a terminal of a stitch by alternately repeating short forward feed and backward feed. An electromagnetically operating means which controls the feeding mechanism applies a pulse wave potential to operate the feeding mechanism. A time period necessary to define the action of the electromagnetically operating means is determined by a multivibrater.

United States Patent Sakashita et al.

[ 51 Oct. 3, 1972 [54] SEWING MACHINE FOR AUTOMATIC BACKTACKING [72] Inventors: Hitoshi Sakashita, Toyota; Tsutomu Mitsui, Chieyu, both of Japan [73] Assignee: Aisln Seiki Kabushiki Kaisha,

Kariya Aichi Peri, Japan 22 Filed: July 9,1970

21 Appl. No.: 53,452

[52] US. Cl ..ll2/203, 112/262 [51 Int. Cl. ..D05b 27/00 [58] Field of Search ..1 12/203, 210, 262

[56] References Cited UNITED STATES PATENJS 3,024,750 3/1962 Winz ..1 12/203 3,363,594 l/1968 Kosrow ..1 12/210 Primary Examiner-James R. Boler Attorney-Pierce, Scheffler & Parker [57] ABSTRACT A sewing machine for automatically making a backtacking stitch against unstitching at a terminal of a stitch by alternately repeating short forward .feed and backward feed. An electromagnetically operating means which controls the feeding mechanism applies a pulse wave potential to operate the feeding mechanism. A time period necessary to define the action of the electromagnetically operating means is determined by a multivibrater.

9 Claim, 6 Drawing Figures SEWING MACHINE FOR AUTOMATIC BACKTACKING BACKGROUND OF THE INVENTION This invention relates to sewing machines which are able to automatically obtain a backward feed for feeding dogs for securing a backtacking stitch against unstitching which would otherwise happen at a terminal of a stitch.

There have been known in the art sewing machines by which the backward feed of fabric may be effected by mechanisms to reverse the forward feed movement of the feeding dog. Further, it has been found that a great many of such mechanisms are used in making a backtacking stitch. However, this conventional method of forming the backtacking stitch by the use of such mechanisms has serious disadvantages, particularly in making the backtacking stitch by alternately repeating short forward feeds and backward feeds of fabric to make a stronger backtacking stitch at the terminal of the stitch. The need for making the backtacking stitch complicates the operation, and reduces the rate of the production of the sewing machine. Additionally, and even more serious, it requires considerable skill to form the backtacking stitch by manipulating the mechanisms to alternately repeat the short forward and backward feeds of fabric, while monitoring the resultant stitch not to maintain a neat appearance.

It is an object of the invention to provide a process for automatically controlling the making of the backtacking stitch.

Another object of the invention is to provide a sewing machine which is able to automatically make a backtacking stitch.

SUMMARY OF THE INVENTION With these and other objects in view, the present invention comprises generally the steps of applying a trigger pulse to an electric control element, applying a pulse to one of switching circuits in the element, energizing an electro magnetically operating means according to the pulse produced by the switching circuits, controlling the positioning of a lever by which the feeding mechanism is controlled and defining a time period in which pulses are produced for controlling the electromagnetically operating means by which the feeding mechanism is in turn controlled. The sewing machine for making such backtacking stitches comprises a lever operatively connected to the feeding mechanism of the sewing machine to convert the forward feed of fabric to backward feed to make the backtacking stitch, a manually operative switch means by which a trigger pulse is applied to the control element, switching circuits in the control element which apply pulses at regular intervals of time to the electromagnetically operating means and in turn control the feeding mechanism, a mechanical part operatively connected with the electromagnetically operating means so as to transmit action of the electromagnetically operating means to the lever and a circuit to define a time period in which pulses are produced to cause the electromagnetically operating means to be energized or deenergized so that the lever may be positioned at the forward feed position or the backward feed position.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of a sewing machine embodying certain features of the invention;

FIG. 2 is a detail side view of a part of the sewing machine;

FIG. 3 is a diagram showing the principal arrangement of parts of the control element;

FIG. 4 is a showing of comparison of the impulse waves produced by parts of the control elements;

FIG. 5 is a view, similar to FIG. 3, showing the principal arrangement of parts of the control element of another embodiment;

FIG. 6 is a showing, similar to FIG. 4, of comparison of the impulse waves produced by parts of the control element of another embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be illustrated in the form it may when applied to a well known and conventional sewing machine 1. Such sewing machine includes a base 2 to present usual hollow upright bracket 3 extending upwardly therefrom, the hollow arm 4 extending, in substantially the usual manner, over base 2 to present the usual front bearing upright 5 immediately over needle plate 6 provided in base 2. Upright 5 may be provided with bores in which may slide presser foot 7 and needle bar 8. In arm 4 may be positioned a shaft (not shown) from which, by suitable mechanism, reciprocating motion is imparted to needle bar 8. A combined pulleyand-hand wheel 9 is attached to the shaft at the end thereof extending beyond arm 4, and provides for association therewith of a belt or other suitable means for driving the sewing machine. A presser foot 10, carried by presser foot 7, cooperates with the usual feed dog (not shown) positioned beneath the base 2 and operable to move in, and be projected through slots (not shown) in needle plate 6 provided for that purpose. Of course, the presser foot 10 may be lifted free of the needle plate 6, in the usual manner, but normally, when such means are released, resilient means drive the presser foot against the needle plate or such fabric as may be positioned on the needle plate.

The usual feed action for the feed dog may be obtained from well known and conventional mechanisms positioned beneath the base and driven by oscillating shaft connected to the shaft on which the combined pulley-and-hand wheel 9 is mounted. The backward feed action may be obtained also from well known and conventional mechanisms (not shown) positioned within the internal space of the upright bracket 3. A lever 11 is placed within convenient reach of the operator to change the forward feed of fabric to backward feed and vice versa. With the lever pulled down, the backward feed is effected while forward feed is effected by restoring it to its upper restposition. The lever may be restored to its upper rest position by a conventional resilient means when it is released from the lower position. Since such mechanisms are well known in the art and the principal object of the invention is to provide a control element, which is capable of incorporation into sewing machines, with but minor changes in such sewing machines, further description of the known mechanisms will not be necessary. A

lever 11 is mounted on the shaft 12 which extends beyond the wall of the upright bracket 3 and is connected with the above described feeding mechanisms so that the backward feeding movement of the feed dog is effected by manually pulling the lever down. When the lever is freed, it returns to its upper rest position by the restoring spring (not shown) as viewed in FIG. 2. Another lever 13 is rotatably mounted on the shaft 12. At both ends of the lever 13, are flanged portions 14 and 15. The lever 11 is always urged by its restoring spring against the flange 14 and the lever 13 is in turn urged by its flange 15 to the upper end of rod 16. The rod 16 is slidably supported in bores provided in U shaped member 17 fixed, by means of screws, to the table 18, and at its lower end abuts one end of bell crank lever 19 pivoted to the member 20 affixed to the table by means of screws, while the other end of the bell crank lever 19 abuts the end of stem 21 of the piston within cylinder 22. Air under a pressure is furnished to the cylinder by way of pipe 23, valve 24, and pipe 25 to drive the piston to the left in FIG. 1. The valve 24 is of conventional type which permits the air to flow into the cylinder or to escape from the cylinder. Since the restoring spring of the lever 11 always urges the stem 21 to the right by way of lever 13, rod 16 and bell crank lever 19, the lever 11 returns to its upper rest position as the piston returns to its rest position. In this condition, the forward feed movement is maintained. As will be noted, the lever may be pulled down while the lever 13 remains at its rest position.

The valve 24 is operable by electromagnetically operating means 27 to permit the air under pressure to flow into the cylinder 22 or to escape from the cylinder. As is evident, when air under pressure is supplied to cylinder 22, the piston will push one end of the bell crank lever 19 to the left to cause it to rotate in a clockwise direction in FIG. 1 and thence the lever 11 will be moved downwardly by means of the rod 16 and lever 13. In this manner, the backward feeding of the dog is effected. When the air is permitted to escape from the cylinder, through the valve 24 and opening 26, the lever returns to its upper rest position by the restoring spring, and the backward feeding movement of the dog is changed to forward feeding movement.

By repeating the above operation a desired number of times, the backward and forward feeds of fabric are alternately repeated and the backtacking stitch which prevents unstitching will result.

The mechanism hereinbefore described can be operable under the control of an electrical control element of the invention which will hereinafter be described in detail.

A manually operable switch 28 is placed within convenient reach of the operator at a suitable position on the table. The switch is grounded at 40 across a capacitor 30 and has two terminals X and Y. Bistable multivibrator 33 is connected with the terminal Y across amplifier 32, while being connected to the electromagnetically operating means 27, such as a solenoid, through five sequentially connected switching circuits, having monostable multi-vibrators, from M1 to MS, a selecting circuit, for instance by a rotary switch 34 to select a desired circuit, to amplifier 35. Leads 36, 37 and 38 connect the switching circuits M1, M3 and MS with the selecting switch 34 respectively. The switching circuit M5 is a additionally connected with the bistable multivibrator 33 by lead 39.

As is evident, upon switching to terminal X, a charge is stored on capacitor 30 which is discharged when the switch is closed at terminal Y. The potential exhibited at terminal Y is applied to the bistable multivibrator 33 after being amplified by amplifier 32. The potential exhibited on the output terminal of the amplifier 32 is of a trigger pulse wave form as shown at (a) in FIG. 4. The characteristic of the bistable multivibrator is such that the input trigger pulse causes the bistable multivibrator to produce a pure square wave of output potential as shown at (b) in FIG. 4. The square wave potential thus produced is thence applied to the monostable multivibrator M1 and actuates it for a time period t1 as shown at (c) in FIG. 4. The switching circuit M2 is actuated in response to a cut off of output potential of the switching circuit M1. The same is brought about in the following switching circuits from M3 to M5 by cut off of output potential of the preceding switching circuit, as shown at (d) to (g) in FIG. 4. The bistable multivibrator 33 is rendered inactive in response to cut off of output potential of the switching circuit M5. The lead 39 transmits the signal of cut off to the bistable multivibrator 33. Thus, one cycle of function of the control element 31 is-terminated, and a time period in which a process for making the backtacking stitch is terminated as hereinbelow more fully described. The principal function of the bistable multivibrator 33 is to serve during the cycle to prevent the control element from having cumulative pulses applied by erroneous manipulation of the switch 28 by the operator.

It will be noted that during activity of the switching circuit M1 current will flow through conduit 36, selecting circuit 34, to the amplifier 35 and thence to the electromagnetically operating means 27 to energize it for a time period t1. From the preceding, it will be further noted that the valve 24 is operated by the energization of means 27 to permit flow of air under pressure into the cylinder 22. This causes the lever 11 to be pulled down and in turn causes the feeding mechanism to effect the backward feed of fabric. When air is released from the cylinder, the piston or stem 21 return to its rest position and in turn allows the feeding mechanism to convert to the forward feed of fabric.

From the preceding, it will further be noted that the backward feed is repeated during the time period 3 times by the embodiment shown at (h) in FIG. 4. If all of the time periods of all of the switching circuits are the same, the backward feed and forward feed can be alternately repeated at regular intervals of time period and thus a neat backtacking stitch results.

According to the invention, the number of the switching circuits may be lessened, as desired, to three or to one by manipulating the selecting circuit 34. Thus, two backward feeds or one backward feed can be effected shown at (i) and (j) in FIG. 4.

Another embodiment of the invention is illustrated in FIG. 5 and FIG. 6. In FIG. 5 and FIG. 6, reference characters, having primes similar to those used in describing the embodiment illustrated in from FIG. 1 to FIG. 4 refer to similar parts of such embodiment.

When a trigger pulse, as shown at (a') in FIG. 5, is applied by manipulating the switch 28' to the monostable multivibrators 41 and M1, these members are rendered active and produce a square wave potential during time periods t and :1 respectively as shown at (b') and (c) in FIG. 6. The square wave potential exhibited at output terminal the monostable multivibrator M1 is applied to the amplifier 35 and thence to the electromagnetically operating means 27', energizing the means 27 Another monostable multivibrator M2 provides a square wave potential during time period t2 as shown at (d') in FIG. 6, in response to cut off of output potential of the mono-stable multi-vibrator M1. The monostable multivibrator Ml thereafter provides the output potentials in response to turn 0B of the output potentials of the monostable multivibrator M2. As will be noted, output square waves appear at the output terminal of the monostable multivibrator M1 at regular intervals of time period as shown at (c) in FIG. 6. That continues until the monostable multivibrator M2 is rendered inoperative in response to cut off of output potential of the monostable multivibrator 41. The time period for making the backtacking stitch is thus determined'by the time period of output of the monostable multivibrator 41.

We claim:

1. The combination with a sewing machine having a power source, stitching mechanism operated by said power source and a feed mechanism driven by said power source for normally advancing material through said stitching mechanism in a forward direction, of means for producing'a backtacking operation of the machine wherein said feed means is periodically reversed by electrically controlled feed reversing means to provide a series of backward and forward movements of the material, said backtacking producing means comprising:

means for producing a trigger potential pulse to initiate the backtacking operation,

means responsive to said trigger potential pulse for producing a square wave' output potential the duration of which determines the duration of the backtacking operation,

a chain of sequentially connected switching circuits each of which produces a square wave output potential pulse when activated, the first switching circuit in said chain being activated by said square wave output potential produced by the means responsive to said trigger pulse, and each of the remaining switching circuits being activated in sequence by de-activation of its immediately preceeding switching circuit; and

circuit means applying the respective square wave output potential pulses from alternately located switching circuits in the chain to and effecting operation of said electrically controlled feed reversing means,

the square wave output potential pulse from the last switching circuit in the chain serving to terminate the square wave output potential produced in response to said trigger pulse thereby terminating the backtacking operation.

2. The combination as defined in claim 1 wherein said means for producing said trigger potential pulse is constituted by a manually operable switch and a capacitor connected therewith such that when said switch is in a rest position said capacitor is charged, and when said switch is activated from its rest position, said capacitor discharges to form said trigger potential pulse.

3. The combination as defined in claim 1 wherein said means responsive to said trigger pulse for producing said square wave output potential is constituted by a bistable multivibrator which produces an output potential that is terminated by termination of the output potential pulse from the last switching circuit in the chain.

4. The combination as defined in claim 3 and further wherein said switching circuits are constituted by monostable multivibrators.

5. The combination as defined in claim 1 wherein said electrically controlled feed reversing means includes a compressed air operated pneumatic cylinder, the air to said cylinder being controlled by an electromagnetically operated valve energized by the output potential pulses from said alternately located switching circuits in the chain.

6. The combination with a sewing machine having a power source, stitching mechanism operated by said power source and a feed mechanism driven by said power source for normally advancing material through said stitching mechanism in a forward direction of means for producing a backtacking operation of the machine wherein said feed means is periodically reversed by electrically controlled feed reversing means to provide a series of backward and forward movements of the material, said backtacking producing means comprising:

means for producing a trigger potential pulse to in itiate the backtacking operation,

means responsive to said trigger potential pulse for producing a first square wave output potential pulse the duration of which determines the duration of the backtacking operation,

first and second switching circuits electrically interconnected such that each circuit is activated to produce a square wave output potential pulse shorter than said first square wave output potential pulse in response to termination of the output potential pulse produced by the other switching circuit thereby to obtain a succession of alternate activations of said switching circuits,

said first switching circuit being also connected to receive said first square wave output potential pulse such that the duration thereof is determinative of the number of alternate activations of said switching circuits,

said second switching circuit being also connected to receive said trigger potential pulse to initiate ac tivation of said second switching circuit,

and circuit means applying the square wave output potentialpulses from one said switching circuits to and effecting operation of said electrically controlled feed reversing means.

7. The combination as defined in claim 6 wherein said means responsive to said trigger potential pulse for producing said first square wave potential pulse and also said first and second switching circuits are constituted by monostable multivibrators.

8. The combination as defined in claim 6 wherein said means for producing said trigger potential pulse is constituted by a manually operable switch and a capacitor connected therewith such that when said 8. cludes a compressed air operated pneumatic cylinder, the air to said cylinder being controlled by an electromagnetically operated valve energized by the output potential pulses from one of said switching circuits.

m-mhn UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3: 95: -9 Dated October 3, 1972 ynventnflg) HITOSHI SAKASHITA, at 8.1

'LL' is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Please correct the heading of the patent to include the following:

(3O) Foreign Application Priority Date July-ll, 1969 Japan 44/5530? n Signed and sealed this 13th day of February 1973..

(SEAL) Attest:

I'IUWARI) M .FLETCIIER,JR. ROBERT GOTTSCHALK Attcsting OFficer v Commissioner of Patents 

1. The combination with a sewing machine having a power source, stitching mechanism operated by said power source and a feed mechanism driven by said power source for normally advancing material through said stitching mechanism in a forward direction, of means for producing a backtacking operation of the machine wherein said feed means is periodically reversed by electrically controlled feed reversing means to provide a series of backward and forward movements of the material, said backtacking producing means comprising: means for producing a trigger potential pulse to initiate the backtacking operation, means responsive to said trigger potEntial pulse for producing a square wave output potential the duration of which determines the duration of the backtacking operation, a chain of sequentially connected switching circuits each of which produces a square wave output potential pulse when activated, the first switching circuit in said chain being activated by said square wave output potential produced by the means responsive to said trigger pulse, and each of the remaining switching circuits being activated in sequence by deactivation of its immediately preceeding switching circuit; and circuit means applying the respective square wave output potential pulses from alternately located switching circuits in the chain to and effecting operation of said electrically controlled feed reversing means, the square wave output potential pulse from the last switching circuit in the chain serving to terminate the square wave output potential produced in response to said trigger pulse thereby terminating the backtacking operation.
 2. The combination as defined in claim 1 wherein said means for producing said trigger potential pulse is constituted by a manually operable switch and a capacitor connected therewith such that when said switch is in a rest position said capacitor is charged, and when said switch is activated from its rest position, said capacitor discharges to form said trigger potential pulse.
 3. The combination as defined in claim 1 wherein said means responsive to said trigger pulse for producing said square wave output potential is constituted by a bistable multivibrator which produces an output potential that is terminated by termination of the output potential pulse from the last switching circuit in the chain.
 4. The combination as defined in claim 3 and further wherein said switching circuits are constituted by monostable multivibrators.
 5. The combination as defined in claim 1 wherein said electrically controlled feed reversing means includes a compressed air operated pneumatic cylinder, the air to said cylinder being controlled by an electromagnetically operated valve energized by the output potential pulses from said alternately located switching circuits in the chain.
 6. The combination with a sewing machine having a power source, stitching mechanism operated by said power source and a feed mechanism driven by said power source for normally advancing material through said stitching mechanism in a forward direction of means for producing a backtacking operation of the machine wherein said feed means is periodically reversed by electrically controlled feed reversing means to provide a series of backward and forward movements of the material, said backtacking producing means comprising: means for producing a trigger potential pulse to initiate the backtacking operation, means responsive to said trigger potential pulse for producing a first square wave output potential pulse the duration of which determines the duration of the backtacking operation, first and second switching circuits electrically interconnected such that each circuit is activated to produce a square wave output potential pulse shorter than said first square wave output potential pulse in response to termination of the output potential pulse produced by the other switching circuit thereby to obtain a succession of alternate activations of said switching circuits, said first switching circuit being also connected to receive said first square wave output potential pulse such that the duration thereof is determinative of the number of alternate activations of said switching circuits, said second switching circuit being also connected to receive said trigger potential pulse to initiate activation of said second switching circuit, and circuit means applying the square wave output potential pulses from one said switching circuits to and effecting operation of said electrically controlled feed reversing means.
 7. The combination as defined in claim 6 wherein said means responsive to Said trigger potential pulse for producing said first square wave potential pulse and also said first and second switching circuits are constituted by monostable multivibrators.
 8. The combination as defined in claim 6 wherein said means for producing said trigger potential pulse is constituted by a manually operable switch and a capacitor connected therewith such that when said switch is in a rest position said capacitor is charged, and when said switch is activated from its rest position, said capacitor discharges to form said trigger potential pulse.
 9. The combination as defined in claim 6 wherein said electrically controlled feed reversing means includes a compressed air operated pneumatic cylinder, the air to said cylinder being controlled by an electromagnetically operated valve energized by the output potential pulses from one of said switching circuits. 